Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 211807
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
207 PM EDT Sat Apr 21 2018

.SYNOPSIS...
High pressure builds over our area through Sunday, then moves
offshore on Monday. Low pressure over the Gulf Coast states tracks
to the east, and slowly impacts the Mid-Atlantic during the mid-week
period. Another area of low pressure may affect the region at the
end of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
An upper air analysis showed a lingering trough in the Northeast
with a closed low ejecting into the Central Plains. There is some
ridging from Hudson Bay Canada toward the Midwest. At the surface,
high pressure is centered from the eastern Great Lakes to the Mid-
Atlantic region.

While surface high pressure is producing some low-level subsidence,
a 250 mb jet positioned just to our north is providing enough lift
within the fast northwest flow aloft to produce some cirrus. This
may thicken a bit at times, but overall lots of sunshine is
anticipated. The 12z Sterling, VA raob shows the cirrus level
cloudiness between 300 mb and 200 mb. Dry conditions are expected
with even some lowering of the surface dew points with ample
boundary layering warming and enough mixing. The winds will be less
than yesterday, but there will still be a breeze.

The hourly temperature, dew point and wind grids were adjusted based
on the latest observations/trends. This includes showing a quicker
rise in temperatures through at least early afternoon for many
places. The dew points were lowered a little for most locales as
some lowering as already taken place given mixing and ample boundary
layer warming.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Northwest midlevel flow will continue tonight as a surface
ridge remains over the region. Some perturbations in the
midlevel flow will approach the region by morning, but there is
little lift with these perturbations. Other than some increased
mid and upper-level clouds, not expecting much in terms of
sensible weather impacts.

This means that temperatures will once again be the primary
forecast concern. Could see temperatures flirting with freezing
again in portions of the area with the growing season underway,
but tonight`s environment will be a little less favorable. For
one thing, if increased cloud cover is present, some radiation
may be re-emitted to the surface (though the height of the
clouds will not hamper nocturnal cooling as much as one may
anticipate). This will be especially true in the southern CWA,
but how far north these clouds persist may prove critical in how
far temperatures fall in more susceptible locations such as the
Pine Barrens. At this point, way too uncertain/marginal to
issue additional frost/freeze products. My suspicion is that no
additional products will be necessary.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
High pressure over the area Sunday slowly drifts offshore Sunday
night, and remains over the western Atlantic Ocean waters
through Monday night before drifting offshore on Tuesday. Plenty
of sunshine and mild, though temperatures will generally be a
few degrees below normal during the day. At night, with clear
skies and light winds, radiational cooling conditions will allow
for colder conditions in the mountains and in the Pine Barrens
of NJ.

During this time, low pressure over the Gulf Coast states will
slowly track to the east, and will be over the Southeast U.S by
Tuesday evening. A warm front just southwest of the region lifts
north through the region Tuesday night as the low tracks north
along the coast.

Though there are rain chances during the day Tuesday lifting
from south to north, the best chances will be Tuesday night as
the low lifts to the north. The low then slowly works its way
north through Wednesday, will be south of Long Island Wednesday
night, and departs on Thursday. Although there may be a period
on Wednesday where locally heavy rain is possible at times, not
expecting a prolonged period of widespread heavy rain with this
system.

Weak high pressure builds through the region late Friday and
Friday night. Another cold front approaches on Saturday.

Temperatures during this time will generally be at or below
normal levels for most of the week, but temperatures trend
warmer towards the end of next week.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of this afternoon...VFR with high clouds. North-northwest to
west-northwest winds mainly around 10 knots.

Tonight...VFR. Clouds above 10,000 feet. Winds becoming light and
variable.

Sunday...VFR with some lingering high clouds. Light and variable
winds, becoming west to southwest less than 10 knots. Winds are
anticipated to become southeast at ACY during the afternoon.

OUTLOOK...
Sunday night through Monday night...VFR. Generally light winds.

Tuesday...Generally VFR. Clouds build from south to north. E-SE
winds 10-15 kt.

Tuesday night through Wednesday...MVFR/IFR in rain and fog. E-NE
winds 10-15 kt.

&&

.MARINE...
Fair weather and sub-advisory winds/seas are expected through
tonight. Northwest winds 10 to 15 kts (possibly gusting to 20 kts or
so) will likely switch to southwest this afternoon before switching
back to northwest or north tonight. Seas should remain near or below
3 feet.

OUTLOOK...
Sunday through Tuesday...Tranquil conditions on the waters with
sub-SCA conditions.

Tuesday night and Wednesday...Rain, fog, and gusty E-NE winds as
low pressure impacts the waters. SCA conditions expected.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...MPS
Near Term...Gorse
Short Term...CMS
Long Term...MPS
Aviation...Gorse/MPS
Marine...CMS/MPS


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